Soil-plant system and potential human health risk of Chinese cabbage and oregano growing in soils from Mn- and Fe-abandoned mines: microcosm assay.

In Portugal, many abandoned mines are often close to agricultural areas and might be used for plant food cultivation. Soils in the vicinity of two Mn- and Fe-abandoned mines (Ferragudo and Rosalgar, SW of Portugal) were collected to cultivate two different food species (Brassica rapa subsp. pekinensis (Lour.) Hanelt and Origanum vulgare L.). Chemical characterization of the soil-plant system and potential risk of adverse effects for human health posed by plants associated with soil contamination, based on the estimation of hazard quotient (HQ), were assessed in a microcosm assay under greenhouse conditions. In both soils, the average total concentrations of Fe and Mn were above the normal values for soils in the region and their concentration in shoots of both species was very high. Brassica rapa subsp. pekinensis grew better in Ferragudo than in Rosalgar soils, and it behaved as an excluder of Cu, Mn, Fe, S and Zn in both soils. The HQ for Cu, Fe, Mn and Zn in the studied species grown on both soils was lower than unit indicating that its consumption is safe. The high Mn tolerance found in both species might be due in part to the high contents of Fe in the soil available fraction that might contribute to an antagonism effect in the uptake and translocation of Mn. The obtained results emphasize the need of further studies with different food crops before cultivation in the studied soils to assess health risks associated with high metal intake.

Tolerance to high Zn in the metallophyte Erica andevalensis Cabezudo & Rivera.

The tolerance to high Zn was studied in the metallophyte Erica andevalensis Cabezudo & Rivera grown in nutrient solutions at different Zn concentrations (5, 500, 1,000, 1,500 and 2,000 µM Zn). Plant growth and nutrient uptake were determined. Metabolic changes were assessed by the analysis of peroxidase activity, organic metabolites related to metal chelation (amino acids, organic acids (malate, citrate) or protection (polyamines). While plants tolerated up to 1,500 µM Zn, despite presenting of low growth rates, the concentration of 2,000 µM Zn was toxic producing high mortality rates. Roots accumulated high Zn concentration (11,971 mg/kg) at 1,500 µM external Zn) apparently avoiding metal transfer into shoots. After 30 days of treatment with high Zn (1,000 and 1,500 µM Zn), the leaves accumulated high levels of glutamine. Short-term treatment with 500 µM Zn, significantly increased the concentration of asparagine and glutamine in roots. Citrate concentration was also considerably increased when exposing roots to Zn excess. Metal immobilization in the root system, low interference with the uptake of nutrients and an increased production of putative organic ligands (amino acids, citrate) might have provided the Zn tolerance displayed by Erica andevalensis.

Evaluation of lead toxicity in Erica andevalensis as an alternative species for revegetation of contaminated soils.

Although revegetation using native flora is a low cost way to stabilize soil and restore the landscape contaminated with metals, little is known regarding the Pb-tolerance of many of these species. For this purpose, we evaluated the tolerance of Erica andevalensis to Pb by growing plants in nutrient solutions with increasing concentrations of Pb (up to 100 microM). Plant growth and different physiological parameters were determined to ascertain tolerance to metal stress. Additionally, an electron microscopy study coupled with EDX-analysis was performed to get clues on the Pb uptake and translocation from roots into stem and leaves. The LOEC (the lowest observed effect concentration) of Pb was 40 microM while the IC50 (inhibition concentration) was 80 microM Pb. Chemical analysis revealed a root > stem > leaf accumulation pattern. There was a severe reduction in fresh biomass and chlorophyll concentration at the highest Pb dose. The SEM-EDX study indicated that Pb was mostly located in root epidermal tissues. The blockage of Pb on the root probably avoided its toxic effects by limiting Pb transport to other tissues.

Stress responses of Erica andevalensis Cabezudo & Rivera plants induced by polluted water from Tinto River (SW Spain).

The effects of Tinto River water on Erica andevalensis growth, biochemical indicators and elemental concentration and distribution were investigated under laboratory conditions. High levels of toxic elements such as B, Fe and S and acidic pH characterized the river water. Plant analysis revealed that the concentration of Al, B, S and Fe increased in all plant organs reaching in some cases values in the toxicity range. Plants transferred into river water stopped growing and stress was manifested by plant water loss, increase in peroxidase activity and decrease of chlorophyll a concentration. Significant decreases of free amino acid concentration were found in shoots and roots of plants grown in diluted river water. The results indicated that Tinto River water acidity and its excess in soluble elements produced altogether severe alterations in roots affecting plant water and nutrient uptake and leading to the massive entry of some metals (e.g. Fe, Al) with toxic effects. Scanning-electron microscopy (cryoSEM and ESEM) observations showed that E. andevalensis had not exclusion mechanisms of Cu, Fe and S therefore it was not able to reduce translocation to aerial parts.

Accumulation and in vivo tissue distribution of pollutant elements in Erica andevalensis.

Erica andevalensis is an endemic shrub from an area in the southwest of Spain (Andalucia) characterized by acidic and contaminated soils. Scanning electron microscopy (SEM) of samples after conventional or cryo-fixation preparation protocols was used for morphological and anatomical studies. SEM coupled with EDX-analysis was employed to localise and quantify different elements within plant parts (leaves, stems and roots) in samples collected in the field. Morphological studies revealed that the species has typical adaptive structures to drought-stress such as rolled needle-like leaves, sunken stomata and a thick waxy cuticle on the upper epidermis. Roots were associated with fungi which formed intra and extra-cellular mycelia. The SEM studies showed that Cu was not sequestrated into the root tissues and was uniformly distributed in leaf tissues. Meanwhile, Pb was only localised within epidermal root tissues which indicates that its sequestration in an external matrix might represent a tolerance mechanism in this species. Iron was uniformly distributed throughout the leaves, while in roots it was predominantly retained on the epidermal cell walls. The exclusion and tolerance mechanisms adopted by this species to survive in mining areas indicate that it can be used successfully in the re-vegetation of contaminated areas.

Effect of nitrogen source on growth response to salinity stress in maize and wheat.

The effect of ammonium and nitrate nutrition on maize and wheat grown hydroponically and salinity stressed was assessed from measurements of growth rate and gas exchange. In both maize and wheat the ammonium-grown plains were much more sensitive to salinity toxicity than nitrate-grown plants particularly when exposed to 60-80 mM salinity. Shoot growth was retarded to a far greater extent than root growth in salinity-stressed plants of both wheat and maize with either nitrogen source. There was no significant decrease of photosynthetic rate in salinity-stressed plants of either species fed nitrate or ammonium, except in severely wilted plants of both species fed nitrate or ammonium at the highest (80 mM) salinity concentration. The same was true for stomatal conductance, transpiration rate and transpiration ratio (water use efficiency). In nitrate-fed wheat, raising the calcium concentration from 2 to 12 mM in the presence of 60 mM salinity produced an 11% increase in growth. This effect is ascribed to improved nitrate uptake due to calcium protection of the nitrate transporter and was not evident in ammonium-grown wheat. Possible reasons for the differential effects of ammonium and nitrate nutrition are discussed.

A Role for manganese in the Regulation of Soybean Nitrate Reductase Activity?

The effect of manganese nutrient levels and light treatments on nitrate reductase activity (NRA) of soybean leaves was studied. Under dark conditions, soybean Mn-deficient leaves showed higher NRA than normal leaves, using the in vivo and in vitro assays. Under light, the differences in activities depended on the incubation media in the in vivo assay, whereas under the same conditions in the in vitro assay the differences observed between (- Mn)- and ( + Mn)-leaves were lower. In leaf homogenates, MV- and FMNH(2)-NR activities were also reduced in ( + Mn)-leaves in comparison to Mn-limiting leaves but DCPIP-NADH reductase was not affected. Apparently, differences in NRA could be localized on the final step of nitrate reduction, though reactivation by the addition of ferricyanide could not be obtained. Partial purification of NADH-NR-inhibitor from both, (- Mn)- and ( + Mn)-leaves, and activity assays showed lower inhibition rates of NRA by those fractions obtained from the Mn-deficient leaves. On the basis of the results obtained, an indirect role of manganese on the regulation of NRA is proposed.